Creep behavior of Grade 10.9 high-strength bolts under and after fire: Fid-Bau Portal

Creep behavior of Grade 10.9 high-strength bolts under and after fire

Lu, Yaoliang / Jiang, Jian / Cai, Wenyu / Chen, Wei / Ye, Jihong

Highlights • Experimentswere conducted on creep behaviour of Grade 10.9 high-strength bolts under and after fire. • The Field & Field model is calibrated for simulating creep behavior of high-strength bolts at elevated temperatures. • The temperature, load ratio and loading duration are key factors affecting the creep behavior of T-stub connections. • High-strength bolts have more obvious creep deformation at high temperatures than high-strength steels. • A reduction factor is recommended to consider the creep effect on determining strength of T-stub connections in Eurocode 3.

Abstract High-strength bolts are widely used in beam-column connections of high-rise steel framed buildings. At the event of a fire, high-strength bolts may experience significant creep in a state of both high stress and high temperature, leading to fracture of connections and even progressive collapse of structures. This paper experimentally and numerically investigates the creep behavior of Grade 10.9 high-strength bolts under and after fire. The creep strain–time curves at different temperatures and stress ratios are obtained using DIC systems. The micromorphology and failure mechanism of high-strength bolts is examined by SEM. The Field & Field creep model is calibrated against test results, and parametric studies are conducted on creep behavior of T-stub connections. The experimental results show that the creep deformation of high-strength bolts is significant at high temperatures, and the creep strain is positively correlated with temperatures and stress ratios. While the creep effect of high-strength bolts after fire can be ignored. The creep-induced fracture of high-strength bolts under fire is in a ductile manner, and that after fire is in a brittle manner. High-strength bolts have more obvious creep phenomenon at high temperatures than high-strength steels, and it is unsafe to directly apply creep data of high-strength steels to high-strength bolts. The numerical results show that the Field & Field model is suitable for characterizing the creep behavior of high-strength bolts under fire with an applicable temperature range of 20–600 °C and stress ratio range of 0.4–0.8. The temperature, load ratio and loading duration significantly affect the creep behavior of T-stub connections under fire conditions. A reduction factor of 0.8 for 500 °C and 0.6 for 600 °C is recommended to consider the effect of creep on the strength of bolts in determining bearing capacity of T-stub connections in Eurocode 3. It is necessary to consider the effect of creep for predicting the fire behavior of high-strength bolts and steel connections, ensuring a safe design.